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Betelgeuse,Cephei Stars,KY Cygni,R136a1and Canis Majoris Stars
Betelgeuse (pronunciation: /ˈbiːtəldʒuːz/ or /ˈbɛtəldʒuːz/[1]), also known by its Bayer designation Alpha Orionis (α Orionis, α Ori),sometimes called as Quonosang,is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining Rigel (Beta Orionis) only rarely. Distinctly reddish-tinted, it is a semiregular variable star whose apparent magnitude varies between 0.2 and 1.2, the widest range of any first magnitude star. The star marks the upper right vertex of the Winter Triangle asterism and the center of the Winter Hexagon.Classified as a red supergiant, Betelgeuse is one of the largest and most luminous stars known. If it were at the center of the Solar System, its surface would extend past the asteroid belt possibly to the orbit of Jupiter and beyond, wholly engulfing Mercury, Venus,Earth and Mars. Betelgeuse is currently thought to lie around 640 light-years away, yielding a mean absolute magnitude of about −6.05. In 1920, Betelgeuse was the first star (after the Sun) to have its angular diameter measured. Since then, researchers have used a number of telescopes to measure this stellar giant, each with different technical parameters, often yielding conflicting results. Current estimates of the star's apparent diameter range from about 0.043 to 0.056 arcseconds. This is a moving target at best, as Betelgeuse appears to change shape periodically. Because of limb darkening, variability, and angular diameters that vary withwavelength, the star remains a perplexing mystery. To complicate matters further, Betelgeuse has a complex, asymmetric envelopecaused by colossal mass loss involving huge plumes of gas being expelled from its surface. There is even evidence of stellar companions orbiting within this gaseous envelope, possibly contributing to the star's eccentric behavior. Only 10 million years old, Betelgeuse has evolved rapidly because of its high mass. It is thought to be a runaway star from the Orion OB1 Association, which also includes the late type O and B stars in Orion's belt—Alnitak, Alnilam and Mintaka. Currently in a late stage of stellar evolution, Betelgeuse is expected to proceed through its expected life cycle before exploding as a type II supernovawithin the next million years. HR 8938 Cephei is a subgiant star near the north celestial pole in the constellation Cepheus.[2] At an apparent magnitude of 5.6, it is near the naked eye limit even under very dark skies.[1] It is about 30 times fainter than the star Polaris.[NB 1] Beta Cephei (β Cep, β Cephei) is a third magnitude star in the constellation Cepheus. It has the traditional name Alfirk (Arabic الفرقة''al-firqah''), meaning "The Flock" (referring to a flock of sheep) This star, along with α Cep (Alderamin) and η Cep (Alkidr), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg.[10][11] Beta Cephei is the prototype of the Beta Cephei variable stars. MY Cephei (μ Cep, μ Cephei), also known as Herschel's Garnet Star, is a red supergiant star in the constellation Cepheus. It is one of the largest and most luminous stars known in the Milky Way. It appears garnet red and is given the spectral class of M2 Ia. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[8] VV Cephei, also known as HD 208816, is an eclipsing binary star system located in the constellation Cepheus, approximately 2,400 light years from Earth.[2][foot 1] A red hypergiant fills the system's Roche lobe when closest to its companion blue star, the latter appearing to be on the main sequence. Matter flows from the red hypergiant onto the blue companion. The red hypergiant, known as VV Cephei A, is currently recognised as the second largest star known, with an estimated solar radius between 1,600 and 1,900.[5][6] Like Betelgeuse, VV Cephei A is plagued by phenomena intrinsic to hypergiant stars that make them difficult to measure with precision. VV Cephei is not entirely spherical, and is surrounded by opaque shells of a highly extended atmosphere, which, coupled with limb darkening, unstable luminosity and other factors, make it difficult to determine its true size. It has a very small parallax, so estimates as to its distance, and consequently, most other deductions made about its nature, have a high margin of error. RW Cephei is an M-class red hypergiant star in the constellation Cepheus. One of the largest stars known, RW Cephei is estimated at 1650 solar radii. RW Cephei, while nearly as large as the orbit of Jupiter, is not as large as other stars in the constellation of Cephus, namely V354 Cephei and VV Cephei A. RW Cephei is also a semi-regular variable star of type LC. Its surface is subject to pulsations in temperature and luminosity. Over the past 50 to 70 years it has varied from classes G8 to M0 with no discernable pattern. Gamma Cephei (γ Cep, γ Cephei), traditionally named Errai, Er Rai, and or Alrai, is a binary star system approximately 45 light-years away in the constellation of Cepheus. Gamma Cephei contains an apparent magnitude of 3.22. The visible part of the system is a stellar class K1III-IV orange subgiant star on its first ascent off the main sequence. It is about 6.6 billion years old (based on Fe/H metallicity).[4] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[5] Gamma Cephei is the naked-eye star that will succeed Polaris as the Earth's northern pole star, due to the precession of the equinoxes. It will be closer to the northern celestial pole than Polaris around 3000 CE and will make its closest approach around 4000 CE. The "title" will pass to ι Cephei some time around 5200 CE. The star has a companion star with a mass approximately 0.409 times that of our Sun.[2] Gamma Cephei B is of stellar mass and is assumed to be of similar age to its primary. It is probably a red dwarf of class M4, 6.2 degrees of magnitude fainter than the K-type primary star.[2] Delta Cephei (δ Cep, δ Cephei) is the Bayer designation for a binary star system located approximately 887 light-years away in the northern circumpolar constellation of Cepheus, the King. At this distance, the visual magnitude of the star is diminished by 0.23 as a result of extinction caused by gas and dust along the line of sight.[3] It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity. V354 Cephei is a red supergiant star located within the Milky Way. It is an irregular variable located approximately 9,000 light-yearsaway from our Sun, and is currently considered one of the largest known stars, with a radius estimate of 1520 times that of the Sun, or 1,060,000,000 km.[3] Assuming the size estimate is correct, if it were placed in the center of our Solar System, it would extend to 7 AU, between the orbits of Jupiter and Saturn. R136a1 is a blue hypergiant star and the most massive star known. It is an estimated 265 solar masses.[2] The star is also the most luminous at 8,700,000 times the luminosity of the Sun.[2] It is a member of R136, a super star cluster near the center of the 30 Doradus complex (also known as the Tarantula Nebula), in the Large Magellanic Cloud. The mass of the star was determined by Paul Crowther et al. (2010).[2] WOH G64 is a red hypergiant in the Large Magellanic Cloud. With 1540 times the radius of the Sun,it is one of thelargest known stars.The size of WOH G64 is estimated at 2,785,000,000 km, or 1,900-2,000 solar radii[1]. KY Cygni is a red supergiant star (spectral class M3.5Ia[2]) located in the constellation Cygnus. It is one of the largest stars known, at about 1,420 or more times the Sun's diameter, and is also one of the most luminous, with about 300,000 or more times the Sun'sluminosity. It is approximately 5,000 light-years away. EZ Canis Majoris (EZ CMa) is a Wolf-Rayet star in the constellation of Canis Major.[1] It has an apparent visual magnitude which varies between 6.71 and 6.95.[2] VY Canis Majoris (VY CMa) is the largest known star and also one of the most luminous. It is a red hypergiant in the constellationCanis Major. It is 1800–2100 solar radii (8.4–9.8 astronomical units) in radius, about 3.0 billion km (1.9 billion mi) in diameter, and about 1.5 kiloparsecs (4,900 light-years) distant from Earth. Unlike most hypergiant stars, which occur in either binary or multiple star systems, VY CMa is a single star. It is categorized as a semiregular variable and has an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m3.Placed at the center of the Solar System, VY Canis Majoris's surface would extend beyond the orbit of Saturn, although some astrophysicists disagree about the star's stated radius, suggesting it is smaller: merely 600 times the radius of the Sun, which would extend past the orbit of Mars.[12]